The present invention relates to an illuminating device and a medium to be illuminated that are a penlight/flashlight for lighting in a dark place and for presenting dramatic effects, with a functionality for effective viewing of a hologram or a holographic stereogram.
Reproduction of a three-dimensional image (holographic image) is made possible with a hologram by its illumination by a reproducing light. Whereas in some cases coherent light such as laser light is required, in the case of the reproduction of a hologram such as a rainbow hologram or a Lippmann hologram incoherent white light such as a halogen lamp or natural light can be used.
Such holograms that allow the use of white light sources as the reproducing light have been widely utilized for purposes such as prevention of forgery of credit cards. Various holographic display devices are also being utilized as devices such as for displaying holographic images for viewing enjoyment.
When a hologram is illuminated by reproducing light, the optical wavefronts of the light from the recorded object during the recording are reproduced, and these wavefronts are viewed as a holographic image by the viewer. What is referred to as the holographic stereogram is another kind of hologram. A holographic stereogram is produced, using as the original images a large number of images obtained by capturing images of the subject sequentially from different viewpoints, by recording on a single sheet of hologram recording medium consecutive exposures of element holograms in the form of strips or dots.
For example, a holographic stereogram that has parallax information only in the horizontal direction is produced by sequentially displaying on the display of a holographic stereogram printing system incorporating a prescribed optical system a plurality of original images that are obtained by sequential image capture of the subject 100 from different horizontal viewpoints and illuminating the displayed images with laser light to execute consecutive exposures to record on a hologram recording medium, as element holograms, the interference fringes generated by interference between the object light, which is modulated as an image, and the reference light.
Because the image information obtained by successive capture of images from different horizontal viewpoints are consecutively recorded in the horizontal direction as strips of element holograms, the collection of image information recorded as a certain part of each element hologram is perceived as a two-dimensional image when seen by the viewer with one eye from a particular position, and the collection of image information recorded as a different part of each element hologram is perceived as a different two-dimensional image when seen by one eye from a different position. Therefore, when the viewer sees a holographic stereogram with both eyes the exposed image record is perceived as a three-dimensional image due to the parallax between the left and right eyes.
In order to improve the legibility of the holographic image with satisfactory reproduction of holograms such as the holographic stereogram described in the preceding paragraphs, the angle of divergence of the illuminating light from the light source that is used as the reproducing light must resemble that of the reference light upon recording the hologram, or it must be parallel light. Therefore, in the reproduction of a hologram the legibility and image quality of the holographic image that is viewed depends on the spatial relationship of the positions of the hologram, the light source and the viewer, as well as on their physical forms.
Therefore, especially in displaying a hologram for the purpose of viewing enjoyment, it is necessary to enable satisfactory reproduction of the holographic image by constraining the relative positions of the hologram, light source and viewer.
As described in Patent Document 1 in the following list, for example, various devices for display of holograms have been proposed that comprise a hologram and a light source for illuminating the hologram with reproducing light.    Patent Document 1    Patent Document 2 (Pen-type viewer)    Patent Document 3 (Holographic wrapping)
There are also various proposals of penlights for use in such events as concerts.    Patent Document 4 (Multi-color penlight)
There are also various proposals of flashlight functionalities that can be used in such scenes as disasters.
These previous holographic display devices required much effort to transport and carry because of their large sizes. The conventional holographic display device described in Patent Document 1 is made to be a construction with great volume and weight due to the complexity and elaborateness of the light source for illuminating the hologram with reproducing light and of the optical system for the improvement of the legibility of the holographic image by constraining the relative positions of the hologram, the light source and the viewer.
Although the portability of the pen-type viewer described in Patent Document 2 is good, it is strictly a device used for the purpose of illuminating a hologram, and has the disadvantage of the extensive handling that is required in setting up for viewing.
Further, the hologram wrapper described in Patent Document 3 is also strictly a device used for the purpose of illuminating a hologram. Although it enables both the holding of the hologram and the light source in optimal relative positions upon viewing and the elimination of the risk of breakage and damage to the surface of the hologram during transportation and carriage, it can hardly be used to function for other purposes such as lighting a dark place or enhancing decorativeness. Other proposals have also been made to illuminate a hologram from a predetermined angle in addition to improving the portability, but none of these provided any decorative effect, to the hologram or when the hologram is not being viewed, through the combination of the light source and an optical diffuser element.
Further, although many types of penlight have been proposed for use in such events as concerts, such as a multicolor penlight of a type described in Patent Document 4 and flashlights and compact penlights for the purpose of use in disasters and in searching for a keyhole in a dark place, they are difficult to use unless the user is trained because of the required understanding of fundamental knowledge about the direction from which the light source must illuminate the hologram.
Therefore, the purpose of this invention is to provide the functionality of holographic viewing, capable of reproducing a good holographic image, to an article that is highly portable and that can be used in the fashion of a flashlight or a penlight or as a decorative light that gives a dramatic presentation effect on people.
In order to realize a solution to the issues described in the preceding paragraphs, this invention provides an illuminating device with the features of comprising a unit for holding a hologram or a holographic stereogram, a light source, a battery and an optical diffuser, of having a member acting as an optical diffuser of the light from the light source, and of providing the capability to attach such hologram or holographic stereogram in a condition such that no member other than those which are optically nearly transparent is placed within the optical path from the light source to the image region of such hologram or holographic stereogram or within the zone of directions from at least 20 degrees above to 20 degrees below, and from 45 degrees to the left to 45 degrees to the right, with respect to the normal to the center of the area of the hologram on the side of the viewer.
In an example of a preferred embodiment, there is a mechanism to switch between a first configuration in which the light from the light source is led into the light-guiding diffuser and a second configuration in which it is made to illuminate such a hologram support unit from a predetermined angle, by joining the carrier for the light source and the light-guiding diffuser, both described in the preceding paragraphs, by means of a movable element.
This invention enables both the functionalities of use as a flashlight or penlight in disasters and emergencies and of use for decorative/dramatic presentation effects in concerts and events, as well as ready placement and maintenance of the relative positions of the hologram and light source in an optimal relationship.
In addition, it enables, by simultaneous or sequential illumination of the optical diffuser element that is placed in the illuminating device, the expression of decorativeness that was not possible by the hologram alone.